1. Field of the Invention
This invention relates to a recording member used for laser beam recording utilizing thermal melting deformation and/or evaporation removal caused by a laser beam and a recording process.
2. Description of the Prior Art
Heretofore, as real time recording methods, there are known various methods such as magnetic recording, electron flux recording and the like. Compared with these recording methods, a laser beam recording method is particularly excellent because said recording method can give a recording free from aging change, a visible pattern recording, and an additional recording of information. As a recording member for laser beam recording, there is used a material which can absorb radiation energy of a laser beam and thereby the thermally melted and deformed and/or evaporated and removed. However, in addition to the above mentioned characteristics, a desirable recording member should have more desirable characteristics such as mechanical strength, stability, reflection rate, absorption coefficient, thermal conductivity, and evaporation temperature (sublimation temperature). In other words, since an information of high density is recorded on a recording member, the resulting recording member has a fine pattern and therefore, it is necessary that the recording member has a mechanical strength sufficient to prevent any mechanical damage. Further, the recording member should be made of a stable material which is free from any changes caused by ambient temperature, humidity, aging change and the like, for the purpose of avoiding any change of the recorded information. In addition, it is preferable that the reflection rate of the recording layer be low, for the purpose of recording by using a weak laser beam as far as possible and enabling the radiation energy of the laser beam to effectively reach the inside of the recording member. The absorption coefficient of the recording layer is preferably a high so as to make an efficient recording. High absorption coefficient results in effective conversion of the radiation energy of the laser beam to thermal energy in the recording layer and thereby, there is easily caused the melting deformation or evaporation removal at the portion exposed to the laser beam.
From a resolving power point of view, it is desirable that the thermal conductivity of the recording layer is small. When the thermal conductivity is large, the heat at the exposed portion transfers to the surrounding portion upon melting deformation or evaporation removal of the portion exposed to the laser beam to melt and partially evaporate the surrounding portion, and thereby the resolving power is deteriorated. It is desirable that the melting point or evaporation temperature (sublimation temperature) is low. The sensitivity to a laser beam is roughly proportional to the melting point or evaporation temperature. The evaporation temperature of the recording layer is preferably low for the purpose of simplifying the laser beam irradiation apparatus and obtaining a high recording speed. In general, it is very difficult to select a material satisfying all the above mentioned requirements.
Heretofore, there have been used metals such as rhodium, and resins. Such metals are excellent from the point of view of their optical density, stability, damage and abrasion resistance, but they have a disadvantageously a high reflection rate (70-90%), a high melting point (about 2000.degree. C.), a high evaporation temmperature (about 4500.degree. C.) and a high termal conductivity (about 1.5 watt/cm.degree. C.) Resins have a low melting point, a low evaporation point and a low thermal conductivity and thereby, can be a recording member having a higher sensitivity than metals, but fail to give sufficient optical density, stability and damage and abrasion resistance from a practical point of view.
For the purpose of obtaining a high density recording, a high resolving power is necessary. Therefore, it is necessary to prepare a very thin recording layer having a uniform thickness (usually less than several microns). However, it is very difficult to obtain such a uniform and thin recording layer of less than several microns from resin material. Even if such resin recording layer is obtained, it does not have a mechanical strength sufficient to be practically used. In the case of using a resin, it is used in a form of containing dyes or pigments so as to absorb the radiation energy of a laser beam. Therefore, when the resin is produced in the form of a very thin film, a sufficient optical density is not obtained and the contrast of the recorded pattern is not sufficient.
As described above, conventional recording materials fail to set a low laser beam output, increase the recording speed and retain a sufficient resolving power in the case of recording a high density information.